Transmission control



Nov. 3, 1931. B. G. BJORNSON 1,330,219

'IFRANSMISSION CONTROL Filed Feb. 1, 1930 2' Sheets-Sheet l //v vw TOP 8. G. BJORNSON ATTORNEY 1931- B. G. BJORNSON TRANSMISSION CONTROL Filed Feb. 1, 1930 ks? QS n m t N t Patented Nov; .3, 931 7;

mm Gs-103mm, 40F 1031;; N; IY..,

I I p p Ass'xenon'iiolnmninnnrnbnn LIIJABQRA- .euronrns mceneonngmn, .onznnw 103K, N;1,1neomomuqno nnw mm:

' msmssm"enema.

7 -i "This 1 ii'DlVEfliiiOIl rel-ates ztoz seleetni'c rwave tt ansmission-systems:and pairtlclilarlyitotwo signaltransmissionsystemutilizing control .e'nengyzunder scontrol of sigiifilstreinsmitted over-the system in edvmcebfz the signals to control: the operation f circuit-control means stone.ormorerpointsrin' the system e An object ofitheiinventionis towimproveth operationizo faaesignal transmissionksysteml includingi therein circuit-"control?means operove *thefisystern. v e v. v

: The: invention is espeeiiallyapplicebletoe system over which twoi-fvva y gtransmissionifof signaling.- energy is requi rediand-lincl uding.as a link eth'erei-n long sectionoftwo -wa=y-'cableof ihi'ghz'iattemmtion and highttransmission time constant, such; as a deep sea submarine: telephone 1 cable. .Signalcentirolled I 2 switch ing devices; whichintheprior patent'artl have been redt'erred to underwvmrious: :names', such as reactinn 'sn'ppl' essors, singing; suppressors, anti-singing- .iievices or echosnppressors, are usiia llyrnssoici ated with the trzinsniittingiajnd receiving paths: at ea chgtenminal of the cable? in .siich syst'einte insure 1 that theasystem is operatti-v jo ztransmit inzo'xilyoneadirectionrat m me s'efiectiivel-y te'preventeinging zind to suppress echoes. :lThi-szisausually nccomsatedanntler-cont-rol-o'f thessignalsktransmitted plishfed-bymaltingthe:switching zrpperetuset I eeeh terminalxresponsive to transmission In onetiir'eetion toiiencler-thecircnitsthereatopg erative .totransmitzm tha.t idirection, and efi'ee'tively to. (disable c the circuits for trans-e mission. ,in. theiopposite direction;

te'm ,snchas filescnibedeabove, the combination of ixjihichfi nay introdnce clifliciilties'jin the epplicationiiof the Signalcontrolled switching apparatus theretoj "'Oneii sthe increasetltime I of transmission overjzthe -.ab1edue ;to its length, another" ispthe' high attenu ation of the other' is the small load capacity er the cable.

The increased timeloftransmission over'the tern may both start talking-within -the"time intervailequal to the=tvansmission time of the cable, resulting in each. subseriber by means i of the switching apparatus, securing control of hisrow'n terminal for transmitting and locking out I the transmission received from the other subscriber. The high attenuation v of the cable necessitating the ,use (if-extremely lnglnpower levels-atthesinput of the system,

the special-requirements as to quality a-ndfi' he lbilCllllliltfltiQIISUffihGSySiZEm have made necessary the use ofnew methods of operation,

and specizil'switching circuits.

In-:generalthe above-mentioned 'difli'cu'lties may be overcome by" circuits designed to give complete eontroliofthe switching circuits at hoth terni-imlsof=the cable to that snbscribei 'short train of control waiv'es of frequencies which ere ili fie-rent "foi' each'termi-I' 'al. This courier'fis utilized to initielly seize control of the circnit control switching'apparatus atthe cable terminalsand at intermediate repeater points in the system for the first talker, this control beingjmeintaineclbythe speech waves when theyiarrive' the switching points.

.e Theterminalwhich firstfstartsitscourier'on :lhere nreseveral characterist cs ,.of a .sys

ingcircuits ofthesystem. r I

aThe circuits .of the present .inventf on are theway,obtains exclusive control-of the talkin thenature of improvements over the circuitsclisclosed in thetwoMethesapplications referred'to above, the e improvements consisting mainly e in means for increasing the efii ciency of thecircuitsand, insimplification of the-circuits enabling a reduction in the amount; of transmission apparatus used therein.

A feature of the invention is a control cir-' cuit of the courier type for a two-way signal transmission system in which the frebeen initially obtained for either terminal of the system. a 1 r V The exact nature and the advantages of theinvention will befclearffrom the following detailed description tliereotwhen read in connection with the accompanying, draw-U,

"amplifier 4; The receiving amplifying path diagrams of cable terminal stations embodyj ings in which FigsQl, 2 and 3 show circuit ing ditterent modifications of the invention. For convenience-the nventlon will be described as applied to a systemforthe two-f way transmission ot'speechwaveabut itis to be understood-that the principles of the in- .vention apply equally as well to systems for ,the two-way-trans'mission of signalwa-ves in generalof frequencies within or outside the speech frequency, range,such as waves representing speech entertainment programs, com

prisin musica-s well. as speech, etc.

7 Figs. 1, 2 and showalternative types of terminal circuits for. a two-waylcable system in which the COUI-IGI'HI thOd of transmisslon control is usedlto; prevent transmission lockouts when two subscribers at opposite ends of the, system both start talking within the time interval equal to the overall transmission time of the cable between terminals.

' Since in each modification of the invention tobe described,theterminal,stations at both ends of the cable, may be substantially idenftical in construction exceptior changes in the design of the courier generators and. the filters necessitated by the fact that the values of the-frequencies of the couriers transmitted fromjthe two terminalsare difierent, it has been deemed sufficient in each case to illus trate only onertermi'nal of the cable system.-

In a cable signaling system having terminal circuits of thetype shown in Fi 1, transmission lockouts are: prevented and in raddis tion the limited freqnencyrange of the cable is utilizedto maximumefficiency tor transmitting signals- V. V

The terminal. station of v Fig. 1 comprises, connected between aflsoiirceof speech ,waves TL,-such as-a'toll telephone line, and a-two way cable TC' of high attenuation and high transmissi'oln time constant, such S as a deep sea submarine telephone cable, a one-way transmitting amplifying-path TA and acneway-receiving amplifying path RA; lhe

output 'ofthe transmitting path-TA andthe input o'fthe -receiving path RA are connected to the east end; or the two-way cable TO by;

means of a three winding transformer or hybrid coil H which cooperates withthe cable TC and the balancing network N to'insure substantial conjugacy between the paths TA and RA. For a similar purpose the input of the transmitting path TA and the output of the receiving path RA arehconnected to the nected between thehybridcoilH andthe hy" brid'coil'H a delay'circuit 1, filters 2 and 3 connected" iniparallel branches of "thetransmitting path, and the one-way transmitting RA coinprises connected between the hybrid coil H and the hybrid coil E the filters 5 and 6 connected' in -.pa'rallel branches of the receivingpath, and the: one-way amplifier .1

Connected across thetransmittin'g path TA between the hybrid coil H andfthe' delaybircuitl is a control Vcircu-it'8comprising-the current-controlled relay-controlling device 9gandthe windings of relays lOto 14 connected in parallel across the output of theccontrol-de vice -.9. A delay circuit 15 is connected be tween the windings ofrelays 12 to 1 and the output of the device 9 tOCl6ltyfltl1e energizati'on ofthose relays in response to the operation ofdevice 9 with respect to the energization of relayslO and 11; 'Relay lOis'designed to operate in response tothe operation ofthe device '9 slightly in advance of the operation of relay 11;" V 7 1 A sourcefltl of alternatingcurrent waves of frequencies" f which are outside the initial speech frequency transmission rangewof the system-:=(temporarilya part of the'usefu'l transmission -freque'ncy' range 5 of the system is utilized for the couriers-frequencies) is adapted to be momentarily connected across the transmittingpathTAat'the' points 1'? in the output of delayz'circuit l by means of switches 18and19 controlled by the operation ofrelays 10 and 1l, lres' pectively.

l Connected: across thd-receivingipath' EA liItersQl' and 2 2, andlthewindings of relays :24 to 30 connected inp'arallel across the output of the device 23. 'A' dela'y'circuit Ellis con nected between the windingsof relays'29 an d 30 and theoutput of the device 23 to delay t re energlz'ation of these relays in response to the operation of, device '28 with respect to the fenergizationcf relays 24:: to 28.

g, i A normally clo sed switch anne to be opened by operation of relay; is. connected in the" transmitting path L TA between the point of connectionofthe control'circuitl 8 thereto and the hybrid coil H A'normally closed-switch 33 adapted tojbe opened by operation of relay-25 -is connected insthc ansmi-tting' path-EA between; the-outputs ot ters 2aand- 3land-ithe; inl'au-t' of amp -"fier 4;;-

j; A? normallyiclosed switch 34 adapteidzto be I iened -:by iop eration ofrelay 12 is connected :1 ethe transmitting path hetneen the; 'L'tput of the {fi-lteriQ; in the zuppe w branch 7 ereof and; the switch" normally open? etc-h,- adapted to zbei closed ;hy operation relay 13 is connected inthe transmitting .thz'TA between: the output-pf filter3 in the Werabranckthereof and; the; switch-32. 1 i p A nonmally open switch--86 adapted to he )sed operation otirelaya27 glEl CQl'l'IlGCllQd the-receiving path JRA between the output I "receiving: amplifier therein and :the; bye id coil H A-normally closed switch 37 a-ptedeto' v be opened hyr operationv ofrelay r-isconnected. in the receiving path RA be 'e'en-fthe output-flof filter 5 in the upper anehzthereofand, the input a of; amplifier I ,nor1 nallytropen switch 58: adapted to be sed bytop'eration ofirel'ay 30-is connected in alreceiving pathBA between the output of 5 filter 6 in thelower branch thereof and a-, input-xofamplifier l. A normally: open :s'w'itchl 39; adapted to be sed-byopera-tionof relay: 28 is connected: the control circuit 20. betvveenthe output' the filter? 22 in the lower branch thereof dztlie 7 input of .control' devices-23. V A non ,ll'y closed switch-4O adapted; to be opened operationotrelay 7 14 is connected in conl :circuit QOUbBlJWGGII vthe output-of. control vicel23 and the-windings of relays 24 to 30. i iormally closed switch 41 -adapte'd-t0 he anedl by operation of relayQdis connected control circuit S'betWeenhthe output of de- 1 circuit-15 and the winding: vofs relays' 12 L- 14;. ,'1 a va 1, :t is apparent that the cablerterm-inal cir=v t-vvhichhasbeen described is of. the form I ich. is known in. theart as semi-biased, that theciizcuit; is normally operative :to ..trans- I i in; one direction (inthis case: from ieast wrestle ndl transmissionr in theoppositexdition isk-dependent upon switching: opera.

PIS; Tlieirelay controlling devices 9rand"23 may; vacuumvtube, amplifier rectifier devices of typge velliknown in the amp; any other ices which will respond" to jalternating rent- "Waves impressed upon their inputs to'ntroltheoperation of svvitchingldevices, h as mechanical relays, in their outputs. .liedelay circuit ,1 maybe a network of "type suitable forrproducing a delay in transmission therethrough of alternating rents in'i'pressed upon its'iinput; for ex-T. ole-Tit inay beja-loyv pass electrical filter" h l as disclosed 'in the' UJS. patents to" npbell Nos. 12275113 and 1522?;114; is d May 22, 1917, an acousticfilter, orasvorkrfor 'a similar/purpose "such? as disied-inaArn'old Patent :No. 1,565,302; issued reinber-=l'-5;l925z .The delay circuits-'1 and;

- at the West term station. I

The east'towest speech Waves receivedover 1 317 and Ethe 7 corresponding ,zdelay 'cirouits'= at the West terminal; stations-are designed tow produce a cvvery rsma ll' delay 0ft secondsninwthe transmission -of currents*therethrough'; i

af- The :delaycircuits '15 and 31 maybe low pass filters or networks 'of any-other type;- su'1table' fOI=-'P I'O (iuC1ng' a delays in rectified; t alternating "currents; transmitted there-'2 .throughm As the :delay'scircuitsdl5 and l I are;merely gutilized to produce a lag'fin the;

operation ofntherelays connectedto theirl-I outputs, they maybe dispensed with ifother I ineansg-such: as'suitable'mechanical design of? the rrelays, are used to v produce the required/z lagn iThe :idelay= circuit; 15' and thewcorre-" r spending delay circuit atthe vvest'terminal; stationareveach desi'gnedto produce atime delay in the I currentstransmitted therethrough c which: is substantially'cqual touthex, I

overall transmission timeofthecable TC be 1 tween-stations which has :beenw-assumed' to bEf' .T secondsr- If the, delay circuitslfi and '31 narenot; used the relays 12 wl-l 1 and the: rre-r lays 2.) and 80 must be delayed in' operationr in response to the operationof'device 9'orade-z vice 23 for v the required length: of'time; by

other meanszy The filters 2, 3, 5, I theband pass typedisclosed 'in:the U. S;

patents to Campbell-mentioned above. The: filters and 5 are .designed'to transnnt frequencie's Within thespeech frequency; range;- and then frequencies correspondlngi to the ,eraton 16 Fat the east terminal station shown, and to suppress frequencies; correspondinga .-to thecourierfrequenciesf generated at the west terminal station (not shown) bya gen erator corresponding-to the {generator :16 at. 5 theeastterminal station. The-courier re-.- quencies f and f be any frequenciescourier frequencies 7% generated: by'the genc outsiderthe initial ;signal frequencyvrange from-eachother;

thefltypes ivelllknown-in the artw The .operation of the system as a Whole Will'now be described referring to Fig. 1 only.

iwhieh, in v the ease being described: isthe init al speech frequency range, and differing It will I be [assumed that speech waves to be transmitted'over the cableTC in the direc t-ion from east toflwest are :being .receivedtat .the east terminal station over the circuit "TL,

and: at that time nos'pieechixvaves to be transmitted over the cable TC from West to east have as yet been received at the West terminal the circuit TL' are impressed on the-transmit ting v path "TA at the east terminal station the ihybridwcoil in, and W111 be dividedibe-v 5 control'circuit 8." The portion divertedinto train of'waves of frequencies f to be trans mitted out; over the path TA. This short control circuit 8 will operate control device 9 therein which in turn will cause the windsame time as relays 12 and 13tofopen the normally closed switch 40 in the output of the ings of relayslO to 14 to be energized.

Relay 10 will operate quickly to close switch 18: to connect the generator 16 across the transmitting path TA at the-points 17. The

comparatively slow operating relay 11 will operate a given instant later to open the switch 19 so as; to disconnect the generator 16'from the path TA. The efiect of this a momentary connection of generator 16 to the transmitting patlrTA will be to cause a short train of waves, which in the following descrlptlon will'be-referred to as the courier f maybe made as shortas is deslred or is neceswillremain operated as long as speech waves "from the sourceTL are being substantially continuously-supplied to the input of control device 9. They are designed so that they will release only after a complete pause in the speech transmission such as would occur at the end of a sentence, and not for the ordinary pauses between words orsyllables.

Due to theretardmgl t f the y .fcircuit 15 in their inputs, relays 1. to 14 will not be energized so as to operate until substantially T seconds after the courier f has been sent out to the cable TC in response to the previous operation of relays 10 and 11. Relay v12 will then operate to open the normally closed switch 34 in the output of filter 2, which filter is designed to transmit waves of frequencies within the ordinary speech frequency range and waves' within the 'fre-" quencyjrangeiof the courier f thus effective- I 1y disabling the transmitting circuit TA for transmitting waves between the output of the delay circuit 1 and the input "of the transnntting amphfier 4 through thefilter 2. Re-

lay 13 will simultaneously operate to close the normally open switch 35 inthe output of filter 3, 'Wl'llCh filter is designed to transmit waves within. the ordinary speech frequency range and wavesof frequencies within the a frequency range of both couriers f and courier f thus effectively closing a transmis sion path for the waves in the transmitting ccircuit TAfrom the "output of delay circuit H 1 through the filter 3 to the input of amplifier .The effect of disconnecting the filter 2 from the transmission path TA and connectmg 1n 1ts place the filter 3 inthe manner described above is to increase effectively the. 7. transmission frequency range of the trans mission path TA T seconds after thecourier f has been transmitted "for the transmission frequency range of the transmitting path TA includes the initial speech frequencies and ,7 the frequencies and f while'previously it man.

compress only those frequencies within the speech frequency range and frequency f Relay 1'4'will operate substantially at the control circuit 20'connected to the receiving *ainplifyingpath RA, so as to prevent false 1 operation of the'relays 24 to by a courier In the manner which has just been described, the east to west speech waves have obtained'coinplete control of the transmitting and receiving circuits of the east termin'alstation, and this control 'will be maintained as long as the east to west speech are being substantially continuously impressed onthe input of control device 9 f 1 The main portion of the east to west speech waves havebeen delayed in transmission to the input of filters 2 and 3 in the transmitting path TA by a small'time interval of 25 seconds This interval needonly be long enough to insure initial operation [of the switching circuits at the west terminalby the courier f before thespe'ech waves arrive there. The delayed speech waves before the operationof relays 12and 13 will be transmitted through the branch of the transmitting path TA comprising the filter 2. After the operation of relays 12 and l3 the delayed speech waves will be transmittedthrough the branch ofthe transmitting path comprising the 'filter'3., The east to west speech waves passed by the filter 2 or 3 are impressed'upon the input of the transmitting amplifier 4.

The amplified speech waves in theou'tput of amplifier 4 will be transmitted to the hybrid coil H1." These waves will be impressed by the hybrid coil H upon the cable TC and transmitted'thereover to the westterminal station, the first speecha waves arrivingat *that' station'substantiallyt seconds after the arrival thereatfof the preceding courier f The manner in which complete control of the transmitting and receiving circuits at the west terminal station is obtained for the east to west speech waves will now be described byreference to the circuitof Fig. 1. That the apparatus to be referred to is that of the west terminal station will be indicated by designating theapparatus thereat with the same characterswhichi designate the corresponding apparatus at the east terminal but followed :by'a'prime mark; i

'. The courier f transmitted over the cable 'TG in'advance of the east to' west speech waves by a'time interval of t seconds-on arrivaraethe; wes terminnsutimwi11 ber pressed Ionthe receivingamplifying path thereat by thehybrid coil .H'i. The 1m.-.

circuitQOf The portion transmitted through the' fil-ter 6 Willbe dissipatedtherein as the" output-of: that filter. is open-circuitedx by the the courier f diverted into rthe control circuit 29 Willbetransmitted "throughi thei filter 21 which isdesigned toitransmit frequencies Within the range ofsf yandi willicause the initial operation. o'ffcontriol .device-,2'3=" in the output thereof to energize ,the windings of relays 24-;- to 30 Relays 24 to 28 will op crate immediatelyand relays 29 and; 30

WiIIoperat-ea short tiniest seconds (Where t" isslightlymore-thanthe relay. timet produced -by-the delay circuit 1) after theoperatio'no f the-formerrelays becau'se of the action ofthedelay circuit 3'1. in delaying for a time interval of t" secondsthesupply-of-current from the output of device to the Win'din of relays 29," and 30.-

cIOSed' 'sW-itch 39/Iin' the input of the trans mitting'path TAf, and relay: operates to open-the normally closed: switch 33;-1located. 1;

:transmitting and "receiving circuits at the eastterminalistationhas been obtained bythe in the same path in the outputfofi'the filters 2-:and 3.; I .Thetransmittingamplifying pat-h TA a't the westterminal station is thus in-G same time thetransmission frequency range of rthetransmittingzpath TAat-the east ter-: minal'stationhas been effectively increased by,addingzthefrequencies f to its;trans1nis-.- sion frequency range. Itis apparent, thereforesthat' as. soon as the. eastj to. West speech itially made inoperatiye to'transmifiwav s fromthe circuit TL! tozthe cable TCI; orto the,input ofcontrol.device 9"; e s Relay 26" operates-substantially at the same time as 'relays2'e5 and 25 to. open'the normally closed switch 41' inthefcontrolcirc'uit 8-; thus efiectively preyentingfalse op eration of relay'le by anyenergywhich'may.

be stored indelay circuitl5 in controlcircuit 8. at the time: switch 325 in the stra-nsmitting path TA" is openedby'operation of'relay 2'4. 1 Relays?! operatessubstantially at thesame time as relays 24:. to 26? to close. the normally open switch '36. inthe output of the receiving amplifying :path :RA iat 'the West. terminal station, thus at that time making thatEpath operative; to transmit; Waves from the; output of thereceiving amplifier7f tothe circuit ReIay QS operates at same time as relays Qetffto 2Zf to;olose thenormally 1 open switch. 39 in the output of filter 22. in" control circ'uitjQO", thusjmakingthat circuit operativeto transmit speech way/es to theinput ofthe control device 23 through A tia llytfseconds after the operation of the're lays 24; to27. Y Relay 29foperatestoopen-the .tl filter Q QQ which filter is designedto trans lit fr quen s w n the" S ee h eq n y.

range." i

Rlays- 29 and 30" 'will" operatesubstam normally closed switchv 37 in the; output; of the branch ofithereceiyingzpath RAf com-. prising the: filter 5f,c thusr-making the receiv ing. path; RAJ inoperative totransmit Waves fromz-the: cablenllGi-throughethe filter. 5 to the) input of: amplifier 7'1. Relay 30- A simul 'taneously operates 'tozclosethe normally open switch '88 in. the output-of the branch ofthe receivin pathRA comprising'the' filter 6; thus'ma ing therecei ving. path RA? op era normally open .switch- 38.. 1 The, portion- 0f tive to transmit Waves from the cable-TC throughthea filter :6 to the: input. oft amplifier'T.' i a I Asthe transmission frequency range of the liltenafi comprises theriniitial speech frequency rangeplu's the frequencies 7% plus thefrez-ceivingpathv RA hasnbeenfefi'ectively increasedatatimeafter thecourier f has ar 7 rived at thewest terminal station about equal to:.the' delay of the speechzwaves behind the courier; This increase: in 1 the .rtransmis'sion frequency rangevof the receiving path R;

atpthei'westterminal station takesplace Sllbfl stantially just after exclusive control of the;

east to westfspeech'waves and atv aboutathe waveshave obtained initial-control of the transmitting and receiving-5. circuits at both terminals; .thetpart ofithe useful: transmission frequency range. of' the;.syst"em temporarily re quirednfor the courier frequency band f .has been: maderimmediately available for ponents included in thefinitial-speech free quency rangefand in addition the frequency bands f andifs-may now be transmitted over the system in that direction;

The speech. .Wayes which are transmitted from the east terminal station over the'cable TO to the-.westterminal station'l seconds behind the preceding courier 1 7%,. {on the arrival atythe latterstation' will also be iIn-'- 'pre'ssedwby the-hybridcoil.H upon thereceiving. amplifying path. RA':.- The inn:

circuit "20" connected) thereto. The portion diverted into the control; circuit 20 Willbe transmittedthrough the. filter. 22'. therein and" impressed on the control device 23 maintainingthat device theoperated condition in-' itiated by thepreceding courier f i The relays 24, to 30' inthe output of thedevice 23 will therefore be maintained energized, as long as the east to west speech waves 7 are i 7 being impressed: substantially continuously 7 upon the input of the device-23.' The transmitting path TA will, therefore,-be maintained disabled and the receiving path RA maintained operative for the same period of time. 1 I

The main portion of the received east to Westspeech waves will be passedby the filter 6 inthe receiving path RA" therein and amplified bythe receiving amplifier 7 therein. Theamplified waves in the, outputof amplifier 7 will then be impressed bythe hybrid coilH ';--.uponf'the circuit TL over which they will beftransmitted to the listening subscriber. 1 V I -Fig. '2 discloses an improved cable termi nal'cir cuit 'of'the'general type disclosed in i Fig. 2 of the copen'dingpatent application of R. C. Mathes, Serial"No; 370 0B4 mentioned above, which terminal circuit is ap- V plicable to cable Systems in Which the twoway cable between-terminals is comparas tively short or :of such low. attenuation that it'is feasible toselect the courier control currents in the presence of simultaneously'out going speech energy. i a

- -The'terminal stat ion of Fig. 2 comprises conne'ctedlbetween a two-way speechtransmissioncircuit TL, which maybe a telephone line and a twoavay cableTC of high attenuation and high transmission-time con- .vstant, such as a deep sea submarine telephone cable a fone-way transmitting amplifying path TA'ancl a one-way receiving amplify,

ving path RA. ;;The outputof the transmitting path TA and the input of the receivingpath RA are connectedfto the east end 'of'thecable TC ,bymeans'of a 'three-winding trans former or hybrid coil H which cooperates with the balancing network N to insure sub- I stantially conjugacy between the paths TA and RA; Fora similar purpose the input of the transmitting path TA and the'output of the "receiving path RA are connected to the circuit TL through the hybrid coiliH having an associated balancingnetwork N A Connected between therhybri'd coils H 'andH 'in the one-way transmitting path TA issadeltiy; circuit 100 and a one-way trans- "mitti ng amplifier 101', and connected between the hybrid coils Hi and H in the recelvmg pathRA is aband-path filter 42 and a a one-way receiving amplifier 43. Connected across the path TAbetwe'enthe hybrid coil and the input'ofv delay circnit'lOOis a control fclrcuit 44Zcomprising a current-.

V 1 controlled relay'cont-rolling device '45; and the windings of relays 46 to 48 connected in parallel to the output of the device 45. The relay ['47 :isfslow operating as CODA- pared to the relay: 46. The operation. of

relay 48. .is delayedwith respect to the operation of relays 46' and 47 by means of the delay circuit 49 connected i between the winding of relay48 and theoutput of. the device45. 'M r A source 50 of alternating current of frequencies f outside the signal frequency range, which in the case-being described is the speech frequency range, is adapted to be momentar ly connected .across the transmitting path TA at the points 61 between the output of relay circuit 100 and the input of the transmitting amplifier 101, by means of switches 52: and 53 respectively controlled by operation of relays 46 and .47 A

. Connected across the receiving path BA between the input of the filter 42 therein and the hybrid coil H is another control circuit comprising filters .55and 56in parallel branchesthereof, a current controlled, relay cont-rolling device 57 in the output of the filters 55 and 56' and the windin s of rela s 58 to 62 connected in parallel to the output of the'device 57.- v '1 Connected in the transmitting path TA between the point of connect-ion'of the-control circuit 44 thereto andthe hybrid cdil H is a normally closed switch 63 adapted to be opened by operation of relay. 58. Connected tion of relay 59. Connected betweenfthe' windings iofrelay 48 and theoutpnt of the delay circuit 49 in control circuit-44 is a normally closed switch a 65 adapted to be opened by. operation ofxrelay 60.

. Connected in receiving pathRAlbetween the output of the receiving amplifier 43 therein and the hybrid coil H is a normally open switch 66 adapted tobe closed by operationof relay 61. Connected in control circuit 54betweenthe output of filters 55 and 56 and the input of control device 57 is a inwthe transmitting path TA betweenthe points 51 therein and thei'nput of the transiniitting amplificr 41. a normally closed switch- 64adap'ted to be; opened by operanormally. closed switch 6'? adapted to be 7 opened 'by'op erationofrelay 48. Connected between the output of filter 56in thecontrol circuit 54 and the switch 67 "in that circuit is a normally open switch 68 adapted to be closed by operation ofrelay' 62.

y It is apparentthatthe cable terminalcircuitof Fig; 2is of the form 'lmown in the artas'semi-biased. v v

The relay controlling devices 45 and 57 arejsimilar to the currentscontrolled, relay controllingdevices?) and 23 of the system of Fig. 1., I I

The delay circuitf40 i's similarto the delay circuit- 1 in thesystem ofFig. 1. but diil'ers therefrom in that it is designed to introduce only a very small delay in; the transmission of currents therethrough V 1 i The filters 42, 55'21Ild.".56 areband :pass filterssimilar. t the filtersf2xandi-t3 oi theisystem gtcftran'smit frequencies withifrthe speech frequency range, and to "suppress tlielicourier frequencies and fil-respectively :genei 'ated bythe generator 5O at thejeast'terminal staremand :the .correspondinig generator rat sthe v awest :terminal 1st ation i (not shown) Thec filtersz at thewest terminal astation correspond- 1 ing t'o, the filters 42 and56z atthe east terminal stations, have the same tr ansmrission range as the latter zfilters: I The courier frequencies vf .and" may lbs any frequencies; outside :the

speech;' frequency {range rand differing from feaclr'otheii."-.The filter 5'5 isa bandpass filter designedyto transmit the courier frequencies af igeneratediattthe westitermin alstation and "to suppress the conrierl'frequencies f; generatedr'atitheieast terminal station. The filter at the west terminal station corresponding to .the' filter 55 Fat; t lieeast; station-is designed to p assthe. courier h-e enc'zes if :and t o: sup- .pr esstl ie courierfrequencies f I The operatio'nofggthessystemv as a whole 7 :miill inoufirl'ie: describedfrefirring to Fig, 2

:only. .i t will :be assumed 'that'i spe'ech waves tore-transmission iromjieastxtoxwst are reenergized. v r I :Ceived first at the.ea'st trminalestation over the circuitlTLg. and at: that; time no 'speech .Wa ves ha-vezbeen received at thewest terminal station for transiiiissiorrover .thetcable TC injtliedirection from west toseast;

i= T he east to Ets est speech -.Waves: fronrsource TL are impressedtupon theztransmitting circuit TA "by "the-hybrid I coiLI-I The impressed currents in the transmittingpathiTA aredivided'betweenthe input of delay circuit 110.0 kandathe ainput fof...the: chhtrolgcncmt 44. The portion divertedvinto control rCllClllt 44 operate tlie' control. device 45 therein causirr'gtliel windings: of relays- 46.;to'48rto be The relay.- 146; i-rvilhoperatez quickly ;to close theESWltClIfiQJSOflS'bO connectithersource 5010f v I wavesof frequencies I 72 iacross the transmit- -ting'; circuit TA'fatllthe pbinfisz .5; 'eparatively s'low operating relay 47 -Wi11 -opcrate fa; given; instant later to a open the-i switch so as to; d sconnect 'theEgener-ator 50 from thetransmitting-circuit TA; Theimomentary cmmeeuoniafrthe :generator 49: to the trans Fmittin'gpath will vcause a ishortitrain of Waves of frequencies 'afg;- which we refer :to hereinafter :as the eourierifi- ,kto be transmitted overltlie "transmitting;circuit-TA; v The courier f may, be made asshort: asis desired or'is necessaiyby the design? H clays-46 and 47. Relays 46f-and '4Z are rsorzdesigned thatgthey l wwill, remain operated? as longxasgspeech waves from the circuit TL arebeing; supplied tothe' ..inpnt== of control device 45:;and so that they :WTill :release only after a {complete pause :in' a conversationand notzfor'gtheulsualzpauses beztweenczword s or-syllables; rr. a

'hundredths of a second,

The :courier f will be amplifiedaby the transmitting amplifier 101 andlthe amplified courier'impressed uponthelcable TG byrthe, :hybridicoil H over which they are transmit ited to the Westtermin'al station tc-establish initial Control ofithe switching circuits there- -atin;a manner which will be described; later.

The relay 48' 'Will operate substantially-T secondsrafter relays'46 and 47 have operated to open ithenormally closed switch 67in the control-circuit 54connected to the receiving tive at thattime totrans'niitwavesincoming over the cable TO to the control device-57.

c The main portion of the east to Westspeech waves received from the circuit TL and "impressed on the transmission path TA through hybrid *coil =H will pass through the delay circuit therein which Will delay the speech Waves in transmissionior a short time t.

The delay circuit 100isas0 designed that the delay time t of thesp'eech Wavesbehind the courier'f e'is onlylong'enough to insurecompletion of the initial operation of switchung apparatus at the. West terminal, station by the preceding courier f betore the speech "Waves arriveat the switching points. The

delay time :t would be in the order' of "a few The delayed: speech waves 7 in theoiitput voiildeila'y circuit 100 are amplified by the ampathR-A, thus making that circuitinoperaplifi'erilOl and transmitted tothe hybrid'coil I H t? The amplified Waves Will be impressed by therhybrid coilH on-the cable TC and transmitted thereover to the West terminal station lagging behind the courier f by a timeanterval-of tseconds- In the manner which hasjust been described. complete control 01": the transmittingandreceiving circuits at,;the east terminal-- station has been" obtained for the east to Wests'peech Waves. a s I 5 The mannerin Which-completecontrol oi the transmitting and receiving circuits at the West terminal is also obtainedgfor the "east: to :West speech Waves-Willnow beidescribed by reference-to the Fig. 2. That the apparatus to I be referred to is that' of the 'West' t'erminal station will be indicated by designating theapparatus thereat With the same characters which designate thecorresponding apparatus at the'east terminal station'butfollowed by aprime mark? "Courier 2m arrival at the'west terminal station is impressed uponth'e receiving path R A' by' the' hybrid coil H As stated abow the filter42 in the receiving path RA and thililter :56fin the control circuit 54 are dcsigned to suppress the' couriervf .The conrierhf will therefore be dii erted intot the control circuit '54 and passed by t-l1?) filter in the upperjbranc'h. thereof, andthen Will :be impressedupon the input ofrhe ;con trol device 57.; The -ccontr0l-dev1ce ,57 T will then operate: to energize the windingsof relays 58 to 62.

' Relay 58 W111. operate to open the nor- I mallyhclosed switch 63' in the input of the operate tojopen'the normally closed switch omitting amplifier 101. Tpath TA at the west terminal will'therefore transmitting path TAy and relay 59 will 64 in the same path in the input-of the trans- The transmitting be disabled so as toprevent the transmission of, any later received west to east speech waves'over the circuit TL from being trans- 'mitted tothe cable-.TG or'to theinput f ,1 controldevice 4:5 to cause false oper t of relays 46' to 48.

- Relay operatesto open the normally 7 closed switch in conrol circuit 14, thus preventing false operation of relay 48'] by any speech energy which may be stored in the delay circuit 49 orin thecontrol circuit 44: at the time theswitch 63" in the input i of the transmitting path TA, is opened by operation of relay'58. Belay 61 will op- 5 erate to close. the normally open'switch 66 a in the output of the receiving path RA, thus making that path operative to transmit in- "coming' east towest speech waves from the cable oTC'to the circuit TL Relay 62 will 7 simultaneously operate to closethenormally open's witch68' in the output of filter 56 in the lo we'r'branch of control circuit 54 thus making that branch operative to transmit 1ncoming' east to west speech wavesithrough filter 56 to the input of control device 57.

Theitransmitting andreceiving circuits of I both the west terminal station and'the east terminal station are now" under complete control ,of' the. east to west speech waves.

"T he control of the westterminal transmitting .i f lOv and receiving circuits initiated by the cou rier f will be -maintained-bythe following speech waves in the following manner.

jThe speech waves transmitted from the east terminal station over the cable TC behind the courier f on their arrival at the west terminalstation will be impressed upon the receiving path RA by the hybrid coil H 7" and will be divided between the input of filter 42 in the main speech transmission path and the inputof the control circuit 54. a The portioniof the impressed speech waves diverted intothe controlcircuit 54 will be passed by the filter 56' therein and impressed 1 upon the input-of control device 57 and serve to maintain that device operated as long as the east to west waves are being substantially continuously received from the cable T0.

The relays 58 to 62 will therefore be maini tained in the operated condition for an equivalent interval of time.

The main portion of the received east to west speech waves will be transmitted by the bandpass filter 42 in the main receiving 7 path RA and amplified bythereceiving amplifier 43' inthe outputfthereof. The amplified east to'west speech waves in: the output of amplifier43 willbe impressed by the hybrid'coil H upon thereceiving circuit TL subscriben a 7 If the speech waves for transm ssion over the cable fromwestto'east are recelved over the circuitTL at the west terminal before speech waves-for transmission from east to west are received overthe circuit TL at the east terminal station,iin a manner similar to that whichhas-beendescribed, the courier wave of frequencies f "which are ioutsidethe speech frequency range and different from the courier frequencies f generated at the east terminal, will obtain exclusivecontrol of the transmitting and receiving circuits at both the west and east terminals, which control will bemaintained by thewest to east speech'w'aves when they arrive atthe control points; i-

It is apparent from the above description of the operation of Fig.2 that the relation of the delay times produced in thetransmission ofthe speech waves-and in the operation of the switching circuits bythe delaycircuits and 49 respectivelyat the east terminal, andby thecorresponding delay circuits at the west te'rminal' station, to the overall transmission time or the cable TC between terminalstations is such-that the terminal station which firstsends out its courier obtains exclusive control of the transmitting and receiving circuits at both" stations, and

thiscontrol. cannot be interrupted until a complete or partial cessation of speech wave transmission. I w a If the oppositely'directed speech waves from thetwo talkers at'the two ends: of the taneously,' but the east talker starts ahead of the west talker, the cable TGIwill be charged with outgoing transmission from the west talker atthe time control-device57 at the and transmitted thereover to the listening system reach the two terminals almostsimulwest station operates. Speechincoming at I thewest station over the cable TC, therefore, will be masked byfthe reflections fromoutgoing speech duringthe time it'takes thecable to dissipate the portion. of the outgoing speech energy. This means that a small amount of the speech maybe lost orodistorted if the system of the invention illustrated in Fig.2 is'used. This loss or distortion will not be sufliciently great to be, troublesome in practice unless a very high grade of quality is desired, especially as such losses will occur relativelyinfrequently.

In the system of Fig. 2 it may be necessary to receive the incomingcouriers f and f at the terminals'of the cablein the'presence of simultaneous outgoing speech energy. The filters and other apparatus in the system should,'there.fore,- be so designed that the courier 'may be separated I from 'the speech energy, and so'thatzthe outgoing courier or intone speech does not, falsely'operatethe receiving control apparatus. 1 This should not be difiicult if thecable TC isnot too long orof too high attenuation, .or if the modulation prodfrequenciesf "and-f a If t uctsof the 1 speech vfrequentriesfall at-the two-way cable between terminals is :so orof such high attenuation that the couriers cannot be properlyuselected. 1n the "presence of simultaneous outgoing speech energy by selection apparatus or ordinary design, lti-lnfly be deslrable toutihze a system employing:terminalicircuits of the kind illustrated n 'F1g. 3, in which means are .pro-

vided for avoiding thenecessity of separating the couriers from the speech. .As indicated:

. sin Fig. 3, theterminal circuitsaresuch that transmitted to the cable untilinitial'control 'of 'the switching circuits atfboth terminals has been obtainedby a preceding courier for oneterminal or the'ot-hen, A a I The cableterminal circuit-of Fig. 3'is an the speech-energy for either direction is not improvement over; thel si'milar circuit disclosed in Fig. 2 in the 'copending MathesapcoilsH and IL a band pa above. V o a in the case of Figs; land h? terminal circuitof Fig. 3 comprises atransmitting amplifyin gpath TA anda receiving amplifying path; RA connectedbetween the t-woeway circuit TLand' the two-waycable TC hybrideoil transformers .H andjH ;equipped with assoc-iatedbalanoing networkshl land I Th transmitting circint- TA comprlses,

connected between the; hybrid coils H 1 andH a delay circuit andf-a oneeway transmitting gamplifier 7 1 and the receiving circuit RA comprises.- connectedgbetween'the hybrid .ter' 72, a' band pass filter 73,jand a one-way tier '14. ,Gofnn'ectedto} the transmitting path TA between the input of the filter 7O and the hybrid coilH' is a'coritrol oilrcuit 5 comthe tlexfiCQTfi and-the windings of relay 79.

A generator-81hr alternating current waves of frequencies f is t'adapted to be momentarily connected through aone-way amplifier' 82to the transmitting path TAjatpoints' .83 between the output of-thetrans'mittin'g ampl fier 71 and the'hybrid'c'oil H by the switches '84 and 85 respectively controlled by operation of the relays-Wand 78.-

tween thefilters 72 and 73 isla control circuit 86 con'norisin g a current-control'ledgrelay controllinsr device 88/00 91. v v Connected in the transmittingpath: TA

87 and the windingsof relays .between theronn'ection thereto of control circuit and the hybrid coil Hgis a normally closed switch 92adapted to; be openedby operation ofrelay 88. Connected in the transmitting path TA betweenthe output of amplifier 71; and. the points 83 is .a normally closed switch 93 adapted to beopened by-operation of relay 89. Connected in control scircuit 75betweenthe output of delay circuit and theavindings of relay 79 is a normally oration of relayf90, Connected in'the-input of thefreceiving path RA between the filter I 72and the hybridcoil H is a normally closed 7 I switch 95adapted to be opened by operation ofrelay 79. Connectedin receiving path RA ibetween'theoutputof amplifier 74 and hybrid coilI-I is a normally open switch 96 adapted to be closed by operation of relay 91..

The west terminal'station (not shown)'jis .identicalwith the east terminal station degscribed above-with the exception of the designiof the-generator corresponding to the generator 81 and the design of the filter corresponding to filter 72.

The relay controlling devices, the band filters and the-other apparatus used'at the two terminalstations aresimilar to the apparatusused for a similar purpose in the carc'uitsof'Figs. 1 and 2. The courier frequencies generated by the generator 81 at the .,east terminal station may be anyfrequencies outside the speech frequency range. The courierfrequencies.7 generated by the gen- "erator at' -the west-terminal station corresp'onding to the generator 81 atthe east'terminalstationmay be any frequencies outside the speech frequency range and differing from thefrequencies f The filter, 73; at the receiving ampliand th corresponding filter "at the west terminal station is designed to transmitfrequencies within the speech frequency range and to suppress the couriere'frequencies f and f The band filter '72 at the-east terminal station *isidesigned to pass frequencies withingthe speech frequency. range and 'the .courierfrequencies f received from the westterminal station, andto-suppress'the courier frequen- -cies f The filter at the west terminal-station corresponding to the filter 72 at the east terminal station is designed to pass frequen 'cies within th'e speech frequency range and the coijirierirequency 7% received from the east terminal station, and to suppress the fr generated at the west courier? frequen cies terminal station. v I

Asthe system operates in a similar manner I i I when the speech transmission-is set up first Connected to the receiving path RA'bB- in the directionfrom ea stto' west as wb en the speech transmission is setup first in the onpotransmission from east-to west are first re-- "east terminal station 7 75 jclo'sedcswitch Qtadapteid to be opened by opceived at the east terminal station over the circuit TL, and that not morethan T seconds late where T is: the overall transmission time of the cable TC between the stations, speech currents are received at thewwest terminalstation for transmission from west to east.

The cast to west speech cwaves fromthe line ,TL are impresse'don the transmitting-circuit 'TA of the east terminal station by the hybrid coil and divided between the input of delay circuit 7 O therein and the-control'circuit 7 5. The portion diverted'into control, circuit 75 will operatethe control device 76 causing the windings of relays 77 and 78 to fbeenergiz'ed firstand substantiallyT seconds ilater (the .delaycircuit 80 being designed to introduce a delay "of T seconds in the transmissionlof currents from'theoutput' of 'thedevice'7 6 to the-windings of relay 79),

the windings of relay 79 will beenergized. I Relay 77 will quickly operateto close the I switch 84so as to connect the source 81- of frequencies across the transmitting circuit TA, and an instant later slow operatingrelay 78 will operate to open the normally closed transmitted out over the transmil zting path QTAjtowa-rds the" cable TC; The courier f 7 may be made as short as is desired or is nec- V v V-e'ssary by the design of relays 77 and 78. The

relays 77 and. 78 are'so designed that they will remain operated as longasfspeechwaves from the circuit TL are being supplied tothe input ofthe control device 76, and so that they will release only after a complete pause in a a between words or syllables; The courier f will'be'impressedj upon the 45 conversation, and not for :the' usual pauses cable TC byfthe hybrid coil Hiarid tran mittedover-the'cable to'the west terminal station, where it. will establish initial control of the switching circuits tliereat jin a manner which'will be describedlater,

seconds after the courier f5 has been transmitt'ed to the cable "TC to open the normally closed switch 95 in the input ofithereceiving path RA, thereby making that path inoperative atth'attime'to transmit waves from the cable TO to the circuit TLyor to the input of the control device 87 so as to'causefalse 'operation of the-relays 88 to, 91." Thus, at

the time thecourier f ar'rivesat' the west terminalstat omthe east to west speechwaves have obtainedcomplete control ofthe transmitting and, receiving circuits at the east terminal station, v i Y a Meanwhile the east t'o west speech waves in theimain transmission-path TA aredeqenergy which may be stored therein at tne time switch 93 opensfrom the output of amiplifier7lfto the cable'TC," Relay:90. operatesto open thenormally closed switch 94 layed' therein thedelay circuit 70 for a time interval of T seconds equal tothe over- "all transmission time of' the cable vTC. The

delayed speech waves are amplified by the transmitting amplifier171f and impressed by the hybrid coilI-I on thecableTC over which they are-transmitted to the west terminal station following the preceding courier by time'int'erval of T seconds. a l f l i The manner in which complete'control of the transmitting and receivin'grcircui'ts at the west terminal is'obtainedby theeastto west speech waves from theeastterrninal will be clear by reference to the correspond ng receiving circuits at the east terminal "station.

That the apparatus to be referred to is that of the west terminal station will be indicated designatingthe apparatusthereat with the same characters used; for designating the cor responding apparatus at the east terminal station but followed by afprimet) mark. The courier f on its arrival at the west terminal station is impressed by theh'ybrid coil H on the input of the receiving path RA'thereat'." lThe impressed -courier f is selected by the 'filter 72. As the filter73 in the main receiving path RA is designed to suppress the frequency 7%,the. courier f passed by filter.72 will be diverted into the control pathf86" in which initiallyoperatesico'ntrel device-87""causing the windings inoperative to transmit waves from the cirlcuit TL to the cable or to the input of .the control device 76 in control'circuit 75f. j'ltelay '89 simultaneously operates to open the normally cl'osedswitchl in output of the transmitting. path TA, thus making that pat-h inoperative to transmit any wfave in the control circuit 75 thus preventing false operation of the relay 7 9' bylenergy 'h'fh b't d an The relay 79 w lloperatesubstant1allyT" 1C may 6 s'ore m d8 ay clrculb 80 in control circuit75 at the time switch 92 inthe input of the transmitting'path TA"is opened. Relay 91 operatessubstantially at the same timeas relays 88 to .90 to close the normally open switch :96 in theoutput of the receiving pathRA, thus making that path'operative' to transmit waves from the 'cable'TC tothe circuit TL. V

The transmitting and receiving circuits at both the east and west terminal stations are now'under the exclusive control of the east to west s'r ieech waves; The control of the west terminal transmitting and receiving" circuits initiated by the courier f Wlll be maintained by-the east and west speech waves when hey fib r of between the; controlci-rcuit 86' and the inputlof, the-bandpass filter 73; The

portion diverted into'control circuit 86 will berimpressed'upon the-input of control device 87 maintaining that devicein-th'e opere ated condition initiated by the preceding' 'courierf as longa's'speefchwaves are being substantially continuously received over the "cable The relays 88 'to 91 therefore will 'be'maintained in the energized condition, and therefore the transmitting pathYTA' will ,be

f-maintained disabled and the receivingpath TA maintained operative for'the same interval of time. a

The main portion 'of the speech waves in the output of filter'ZZ 'will be passed by the ba'ndpa'ss filter73f infthe receiving.path BA. The passed'waves will be amplified by amplifier 74f 'and'transmitted from theout- ;;put thereof to the hybrid coil H and impressed thereby onthecir'cuit' TL over which they, will be transmittedito the listening sub,- scriber. f v It is readily seen'thatfbecause of the par ticular relation of the delays produced in the transmitted 'fwaves the delay circuits 70, 80, 70' and80 at the 'east-and west ter-V mingle respectively-t0 the overall transmissiontime of the cable TC, that whichever terminal first sends out its courier over the cableiwill gain eXclusivecontrolof both sets of terminal apparatus. Because speech energy from each stationls not impressed upon ithecabIeTC until after the initial operation of the switching apparatus-at thef'far termi- 11511 by the first courier tqbe t'ransmitted, the incoming courier needfn'otfbe selected in the a presence of simultaneouslyoutgoing speech energy and, therefore, there-will be no loss of speech because of interference therewith. Itisto be understood that the invention is not limited'to the particular circuits and the details of the particular terminal stations illustrated and'described, as numerous modifications thereof may be" made by persons skilled :intheart without departing 'from the spirit and scope ofthe invention.

Although in the particular embodiments of thejinvention which nave-just been dej scribed, mechanical relays have been shown operating movable switches to close or open circuitthese paths, the invention is not limited to the particular conditioning means I shown. For example, withinfthescope of the invention', the transmission paths may be: ef-

fe'ctively disabled byshort circuits or loss networks inserted in the paths, controlled by current controlled relays. v Stationary devices having no movable elements may be employed in place-of the mechanical relays shown, for example,ivacuum tube relays,such

as disclosed in 'Crisson Patent 1,647,212 issued-November 1, 1927', or in an article by'C.

AJBeersand G. T. Evans in theiInstitute of P. 0. Electrical Engineers (London), vol. 20, pages 65 to 7 2 inclusive, published in 1 920;

-What iscl aimed is: a 1, Q In combination, a transmission path, means in said-' path normally preventing transmission thereover'of waves of certain frequencies, 'whil.e allowing transmission 'thereover ofother frequencies, means for transmitting over said path waves of sad other frequenc1es,"and means for condltloning said pathto transmit waves of said certain frequencies, a predetermined time" after the waves of said other frequencies have beenltransmitted thereover;

I Incombination, atransmission path, 'circuit-control 7 means therein responsiveto waves transmittedover said path, means normally preventing transmission over saidpath of waves of certain frequencies while allowing-transmission thereover of waves of other frequencies,means fortransmittingfover;said

path Waves of'said other frequencies to actuate saidJoircuit-controlmeans, and means for waves of saidotherfrequencies as soon as saldclrcuitecontrol means have been acturendering said path operative" to transmit V 3; In icombination'ya transmissionxpath supplied from a source of waves of a range of frequencies, circuit-control means in said I path responsive to waves transmittedthereover, means in said path normally 'preventing transmission thereover ofwaves of certain frequencies in said range, while allowing transmission thereover of other frequencies with -n said range,means for transmitting over saidpath waves'ofsaidother frequencies toactuate saidcontrolmeans, and means for frequencies; as soon as said "circuit-control frequencies, 'azc'ircuit-controlmeans in said path responsive to waves transmitted thereover, means .in said path normally preventing -transmlssion thereoverof waves. of cert'ainfrequencies in said range while allowing transmission ofiiotherwavcs in said range, for conditioning the transmission paths for f path from said source for transmitting over -saidp'atlr'wa ves of said other frequencies to actuate said circuit-control means, means also responsive "tojthewaves received from said meansres'pon'sive to waves received by said source for: conditioning said path totransmit supplied waves ofboth saidcertain and said other'frequenclesas'soonfas sa1d circult-conc trol means have been'actuated by the trans,-

mitted waves ofsaid other, frequencies.

e :1 :5. A terminalstation for a two-way signal transmissioncircuit, Comprising a one-way transmitting path supplied froma source of.

signals of a range 'ofjfrequencies and one way receiving path, means .normally prevent- .ing 's'aiditransmitting path from transmitting to; said two-way circuit Waves of cert'ain fre quenciesi within said range while allowing transmission :thereto of, waves of other vfreoperation by therwavesi received over said two-Way circuit. 7 v 6. A term nal-stat on'foratwoeivay' trans miss on circuit. comprising a transmittlng two-way circuit, meansinsaid receivingpath normally preventing transmission thereover;

'ofwavesof certain frequencies while allowmg transmission of Waves of other .fre-

Jq'uencies, and means responsive to waves received over said two-way: circuit for-{renderiing said receivingapath operative to transmit waves of said certain andsaidpother'freg quenci'es. a

{7.2In combination, atwo-way signal-transmission medium of limitedusefultransmisesionafrequency range and terminal circuits therefor eachcomprisingatransmitting cir- -icuit,=a receiving circuit," a control path connected to said transmission medium :and responsive to wavesreceived thereoverto alter the transmission: characteristics of-said transmitting and, said receiving v circuit, means responsive to the initiation of signals :in said transmitting circuit to be transmitted "of for transmitting over said medium to said 7 other'ter'minal, a's'hort trainof control waves Fof frequencies differing for each terminal and within saldlnnited frequency range, means ing transmission to saidmedium ofwaves of frequencles withm the frequency range of the control waves transmittedfrom the other c fterminal and means also responsive, 7 to i the cab ing said control path;

quencies: within said range, circuit-control path and a receiving path'con'nect'edto, said over said medium to the otherterminal there 111 said transmitting path. normally preventsignalsto be transmitted over said medium for conditioning said transmitting path to transmit. waves of substantially all frequenciesWithi-n said limited frequencyrange, and for A substantially slmul'taneouslyi CllS- 8: ;Tl16 combi f ation ofcIaimTand in which the lastrmentioned means operates to condi- 'tion sa1d transmitting clrcuitto transmit substantially all frequencies within said limited frangeiandto disable said: control path at a time after-the controliwaves have-been transl 'mittedt-o' said;mediumsubstantially equal to the overall transmission timeof the medium bctween terinina-ls.*.-

"1; Y r 9, lncombination, a two-'way'tr'ansmission -.mediumof limited useful-. transmission frequency range and. terminal circuits therefor eachcomprising anorma-lly operative transjmitting patln a normally fdisabled receiving I pad 1 a control. c1rcu1t-{connectedto sa1d medium-aneans responsive to the initiation of signals in saidtransmittingjpath to. be transmitted over said medium to the other terminal thereof for -Dransmittingbver said medium and in'ac-rance ofsaid'fs-ignals a short train Of'H-Control' wavescf frequencies Within said frequency range'ai-iddiffering for each terminal; means also responsive to said signalsto he transmt' d, and independent of said control'waves'fo'r alteringthe transmission characteristics of said transmitting 133th and'said control circuit, means'in said receiving circuit normally preventing; the transmission thereover; ofiwaves, ofgfre'quencies; cor-responding to those of the controlrwa ves transmitted from thef'otherterminal and means in said control-path and responsive towaves received over said 'medium for effectively disabling said transmitting pathand the means responsive to, Signalsjin said transmitting path for .tran'smittingcontrol waves and for altering the transmission characteristics ofsaid trans- "mitting pat'h and of said control circuit, and

for. thereafter renderingsaid receiving path onerativeto transmit substantially all waves of frequencies within the limited frequency range ofsa-idmedium. a a I 10 The system; of claim 9 and inwhich said means responsive to signals in said transmitti n g" path for altering thetransmissi on char acteristicsof said transmittingp'ath and said control circuitoperates ata time after the transmissionsof said train officontrol Waves to said-medium substantially equal to' the overall' transmission of said medium between terminals. 3 I .7

11. Thesystem o'fcla1m9 and ingwhichsaid means responsiveto' si'gnals my said transmitting path for alteringthe' transmission char acteristics of'said transmitting path and said control circuit: operates at a time after the transmission {of saiditrainofcontrol waves to 'said mediui'n'i substantially equal to the ,overall transm ssion of, sa1d medium between terminals and in which said means "for rendering said receiving path operative to trans mit' substantially all waves of frequencles within the limited frequency range of said medium operate at a timeiafter said waves are signals to be transmitted over said mediumf for sending out oversaid transmitting circuit to said medium and in advance ofthe signals, a control wave of frequencies different for each terminal circuit and within,

said limited frequency range, means in-said.

receiving circuit normally preventing transmission'thereover of waves of frequencies within the frequency range of the control waves transmitted from the other terminal, and means connected to said control'circuit and responsive to waves received thereby from said medium for disabling said transmitting circuit fortransmitting waves to.

said medium, and thereafter conditioning said receiving circuit to transmit Waves of all frequencies within said limited frequency range of said medium.

13. In combination, a two-way transmission medium of limited frequency range having an overall transmission time of T seconds, and a terminal circuit'at each end of said medium comprising a transmitting circuit a receiving circuit and a control path connected to said medium, means responsive to the initiation of signals in said transmitting circuit to be transmitted oversaid medium for sending over said transmitting circuit to said medium and in advance of said signals, a control Wave'of frequencies diflerent for each terminal and within said limited frequency .range,'means in said transmitting circuit and insaid receiving circuit normally preventing transmission thereover of waves of'frequencies Within thefrequency range of the control wayes transmitted from the otherterminal, and "means also. responsive to the signals to betransmitted for conditioning said transmitting circuit substantially T sccondsafter the initation of said signals therein totransmit to said medium waves of substantially allfrequencies within the limited frequency range thereof, and

for substantially simultaneously disabling,

said control path, and means in said controlflpathrresponsive to waves received over said medium for effectively disabling said transmitting circuit and the control wave transmitting means and substantially at the same time rendering said receiving circuit operative to transmit waves of substantially all frequencies in said range. I

14. A terminal circuit for a two-Way signal transmission line having an overall transmission time of T seconds, comprising a normally operative transmitting circuit, a normally disabled receiving circuit, a control path connected to said line, means responsive to the initiation of signals in said transmitting circuit for sending out there- Y over to said line and in advance of said sig-] nals by a time lnterval of t seconds,.where z is small in comparison with T, a control, Wave of a frequency outside-the frequency :range of thesignals to be transmitted over said line, means in said control path and responsive to. waves received therein over said line for disabling said transmitting circuit and substantially simultaneously rendering said receiving circuit operative and means responsive to said signals in said transmitting circuit and independent of said control wave for disabling said control path substantially T seconds after said control wave has been sent out, and for maintaining said control path disabled during the duration of substantially continuous transmission of said signals in; said transmitting circuit. 15. A terminal circuit for a two-way signal transmission line having an overall transmission time of T seconds, comprising a normally operative transmitting circuit, a normally disabled receiving circuit, a control path connected to said line, means responsive to initiation of signals in said trans mitting circuit for sending out to said line a control'wave of a frequency outside the frequency range of said signals, means for delaying transmission over said transmitting circuit to said line of said signals behind said control wave for substantially T seconds, means also responsive to the signals in said transmitting circuit and independent of said control wave for disabling substantially T seconds aft-er said control wave has been transmitted to said line, said control path and said receiving circuit for receiving waves from said line, and means in said control path and responsive to waves received thereby from said line for disabling said control path, disabling means and said transmitting circuit, and for substantially simultaneously rendering operative said receiving' circuit. 1

In witness whereof, I hereunto subscribe my name this 31'dayof January, 1930.

BJORN Gr. BJORNSON. 

